Stability of an expanded trinucleotide repeat in the androgen receptor gene in transgenic mice.

The expansion of trinucleotide repeat sequences underlies a number of hereditary neurological disorders. To study the stability of a trinucleotide repeat and to develop an animal model of one of these disorders, spinal and bulbar muscular atrophy (SBMA), we have generated transgenic mice carrying either the normal or expanded repeat human androgen receptor (AR) gene. Unlike the disease allele in humans, the AR cDNA containing the expanded repeat in transgenic mice showed no change in repeat length with transmission. Expression of the SBMA AR was found in transgenic mice, but at a lower level than normal endogenous expression. The lack of a physiological pattern of expression may explain why no phenotypic effects of the transgene were observed.

Proteolipid protein is necessary in peripheral as well as central myelin.

Alternative products of the proteolipid protein gene (PLP), proteolipid protein (PLP) and DM20, are major components of compact myelin in the central nervous system, but quantitatively minor constituents of Schwann cells. A family with a null allele of PLP has a less severe CNS phenotype than those with other types of PLP mutations. Moreover, individuals with PLP null mutations have a demyelinating peripheral neuropathy, not seen with other PLP mutations of humans or animals. Direct analysis of normal peripheral nerve demonstrates that PLP is localized to compact myelin. This and the clinical and pathologic observations of the PLP null phenotype indicate that PLP/DM20 is necessary for proper myelin function both in the central and peripheral nervous systems.

Remarkable intron and exon sequence conservation in human and mouse homeobox Hox 1.3 genes.

A high degree of conservation exists between the Hox 1.3 homeobox genes of mice and humans. The two genes occupy the same relative positions in their respective Hox 1 gene clusters, they show extensive sequence similarities in their coding and noncoding portions, and both are transcribed into multiple transcripts of similar sizes. The predicted human Hox 1.3 protein differs from its murine counterpart in only 7 of 270 amino acids. The sequence similarity in the 250 base pairs upstream of the initiation codon is 98%, the similarity between the two introns, both 960 base pairs long, is 72%, and the similarity in the 3' noncoding region from termination codon to polyadenylation signal is 90%. Both mouse and human Hox 1.3 introns contain a sequence with homology to a mating-type-controlled cis element of the yeast Ty1 transposon. DNA-binding studies with a recombinant mouse Hox 1.3 protein identified two binding sites in the intron, both of which were within the region of shared homology with this Ty1 cis element.

The molecular pathogenesis of Pelizaeus-Merzbacher disease.

In 1885, Pelizaeus described 5 boys in a single family with nystagmus, spastic quadriparesis, ataxia, and delay in cognitive development. In 1910, Merzbacher reexamined this family, which then included 14 affected individuals, including 2 girls, and found that all affected family members shared a common female ancestor. Also, he noted that the disease was passed exclusively through the female line without male-to-male transmission. Pathological analysis of brain tissue from one affected individual showed that most of the central white matter lacked histochemical staining for myelin, although there were occasional small regions of preserved myelin, giving the sections a "tigroid" appearance. The description of this family provides the clinical, genetic, and pathological basis for Pelizaeus-Merzbacher disease (PMD): an X-linked disorder of myelination classically characterized by nystagmus, spastic quadriparesis, ataxia, and cognitive delay in early childhood.

Balo's concentric demyelination diagnosed premortem.

We report the first antemortem diagnosis of a lesion showing Balo's concentric sclerosis. A patient with a progressive left hemiparesis had a ring-enhancing, low-density right frontal white matter lesion. On myelin stains of a needle biopsy, alternating demyelinated and myelinated zones in the white matter were diagnostic of concentric sclerosis. The patient improved with prednisone therapy, but relapsed temporarily 15 months later. CT and MRI showed additional lesions, but no features unique to this process. He remains alive and employed 3 years after diagnosis.

Prion disease (PrP-A117V) presenting with ataxia instead of dementia.

Gerstmann-Sträussler-Scheinker disease (GSS) is caused by several different point mutations of the prion protein (PrP) gene, each of which generally produces a distinct clinical phenotype. An ataxic form of GSS is genetically linked to a mutation at codon 102 (CCG-->CTG) leading to the substitution of leucine for proline, while a "telencephalic" variant of GSS, in which dementia is the predominant symptom and ataxia is minimal, has been described in two kindreds with a mutation at codon 117 (GCA-->GTG) resulting in the substitution of valine for alanine. In this report, we present a family with ataxic GSS that has, however, the same mutation at codon 117 as is present in the telencephalic variant of GSS. Other than an additional silent mutation (GCA-->GCG) at codon 117 on the normal allele, there were no other mutations detected. At the polymorphic codon 129, valine was encoded by both alleles in the proband that we studied. Why this family with prion disease (PrP-A117V) should present with ataxia instead of dementia, which was found in two previously identified families with the same PrP gene mutation, remains to be established.

Light and electron microscopic immunocytochemical localization of clathrin in rat cerebellum and kidney.

The precise cellular and subcellular locations of coated vesicle protein, clathrin, in rat kidney and cerebellum have been visualized by immunocytochemical techniques. In the renal tubular epithelia, clathrin-positive products were found on both free ribosomes and on those attached to rough endoplasmic reticulum (RER) and the nuclear envelope. No clathrin was observed in the cisternae of RER or the Golgi apparatus. Clathrin-positive reaction products could also be seen on coated pits, coated vesicles, Golgi-associated vesicles, basolateral cell membrane, the ground substance, and in the autophagic vacuoles. In cerebellar Purkinje and granule cell bodies, reaction products were seen localized on coated vesicles, on the budding areas from the Golgi-associated membrane and Golgi-associated vesicles. Furthermore, the membrane of the multivesicular body, the bound-ribosomes, and the ground substance were also stained. In the myelinated axon, the clathrin appeared to be concentrated on certain segments and seemed to fill in the space between neurotubules and some vesicles. In certain synaptic terminals clathrin was often seen attached to presynaptic vesicles, presynaptic membrane, and post-synaptic membrane. However, in most mossy fibers, some synaptic vesicles were not stained. These observations suggest that clathrin is synthesized on bound and free ribosomes and discharged into the cytosol where it becomes associated with a variety of ground substances and assembles on coated pits, coated vesicles, Golgi-associated vesicles, presynaptic vesicles, and pre- and postsynaptic membranes. Clathrin may be finally degraded in autophagic vacuoles.

Correlation between weakness and axonal loss in patients with CMT1A.

We have developed a protocol to measure the progression of disability in patients with Charcot Marie Tooth (CMT) disease, particularly CMT1 over a several year period. Because CMT1 is a chronic disease, the natural history of changes occurring in such a brief period are not well understood, making clinical trials for CMT1 patients difficult to evaluate. We hypothesize that weakness in CMT1 correlates with axonal loss secondary to the abnormalities in Schwann cell myelin gene expression, which cause the disease. To test this hypothesis, we elected to carefully evaluate CMT patients by various modalities to measure strength, sensory loss, and axonal loss and demyelination and to compare these modalities to determine whether they correlated with findings on clinical examination. As suspected, patient weakness correlates more with secondary axonal loss than with demyelination, even though the primary abnormality in CMT1 is demyelination.

Peripheral neuropathy caused by proteolipid protein gene mutations.

Pelizaeus-Merzbacher disease (PMD) is a dysmyelinating disorder of the central nervous system typically caused by duplications or missense mutations of the proteolipid protein (PLP) gene. Most investigators have found that peripheral nerve function and structure is normal in PMD patients. We have found that null mutations of the PLP gene cause demyelinating peripheral neuropathy, whereas duplications and a proline 14 to leucine mutation do not affect nerve function. A family with a nonsense mutation at position 144, which affects only PLP but not the alternatively spliced gene product DM20, has a very mild syndrome, including normal peripheral nerve function. Our findings suggest that DM20 alone is sufficient to maintain normal nerve function and that there may be domains of PLP/DM20 that have a relatively more active role in the peripheral nervous system compared with that in the central nervous system.

Assessing abnormal iron content in the deep gray matter of patients with multiple sclerosis versus healthy controls.

BACKGROUND AND PURPOSE: It is well known that patients with MS tend to have abnormal iron deposition in and around the MS plaques, in the basal ganglia and the THA. In this study, we used SWI to quantify iron content in patients with MS and healthy volunteers. MATERIALS AND METHODS: Fifty-two patients with MS were recruited to assess abnormal iron content in their basal ganglia and THA structures. One hundred twenty-two healthy subjects were recruited to establish a baseline of normal iron content in deep GM structures. Each structure was separated into 2 regions: a low-iron-content region and a high-iron-content region. The average phase, the percentage area, and the total phase of the high-iron-content region were evaluated. A weighting was also assigned to each subject depending on the level of iron content and its deviation from the normal range. RESULTS: A clear separation between iron content in healthy subjects versus patients with MS was seen. For healthy subjects 13% and for patients with MS 65% showed an iron-weighting factor >3 SDs from the normal mean (P < .05). The results for those patients younger than 40 years are even more impressive. In these cases, only 1% of healthy subjects and 67% of patients with RRMS showed abnormally high iron content. CONCLUSIONS: Iron-weighting factors in the basal ganglia, THA, and the midbrain appeared to be abnormal in roughly two-thirds of patients with MS as measured by SWI.

Iron stores and cerebral veins in MS studied by susceptibility weighted imaging.

AIM: In this paper, we seek to determine whether the iron deposition as seen by susceptibility weighted imaging (SWI) in the basal ganglia and thalamus of patients with multiple sclerosis is greater than the iron content measured in normal subjects (individuals unaffected by multiple sclerosis). As increased iron content may result from increased venous pressure, such information would add credence to the concept of Zamboni et al (1) that MS is caused by chronic cerebrospinal venous insufficiency. METHODS: Fourteen MS patients were recruited for this study with a mean age of 38 years ranging from 19 to 66 year-old. A velocity compensated 3D gradient echo sequence was used to generate SW images with a high sensitivity to iron content. We evaluated iron in the following structures: substantia nigra, red nucleus, globus pallidus, putamen, caudate nucleus, thalamus and pulvinar thalamus. Each structure was broken into two parts, a high iron content region and a low iron content region. The measured values were compared to previously established baseline iron content in these structures as a function of age. RESULTS: Twelve of fourteen patients had an increase in iron above normal levels and with a particular pattern of iron deposition in the medial venous drainage system that was associated with the confluence of the veins draining that structure. CONCLUSION: Iron may serve as a biomarker of venous vascular damage in multiple sclerosis. The backward iron accumulation pattern seen in the basal ganglia and thalamus of most MS patients is consistent with the hypothesis of venous hypertension.

X-linked distal hereditary motor neuropathy maps to the DSMAX locus on chromosome Xq13.1-q21.

OBJECTIVE: To clinically characterize and map the gene locus in a three-generation family with an X-linked adult-onset distal hereditary motor neuropathy. METHODS: Microsatellite markers spanning the juvenile distal spinal muscular atrophy (DSMAX) locus were genotyped and analyzed using genetic linkage analysis. The promoter, untranslated and coding region of the gap junction beta1 (GJB1) gene was sequenced. Nine positional candidate genes were screened for disease mutations using high-resolution melt (HRM) analysis. RESULTS: The family showed significant linkage to markers on chromosome Xq13.1-q21. Haplotype construction revealed a disease-associated haplotype between the markers DXS991 and DX5990. Sequence analysis excluded pathogenic changes in the coding and promoter regions of the GJB1 gene. Additional fine mapping in the family refined the DSMAX locus to a 1.44-cM interval between DXS8046 and DXS8114. HRM analysis did not identify disease-associated mutations in the coding region of nine candidate genes. CONCLUSION: We have identified a family with adult-onset distal hereditary motor neuropathy that refines the locus reported for juvenile distal spinal muscular atrophy (DSMAX) on chromosome Xq13.1-q21. Exclusion of mutations in the coding and regulatory region of the GJB1 gene eliminated the CMTX1 locus as a cause of disease in this family. Nine positional candidate genes in the refined interval underwent mutation analysis and were eliminated as the pathogenic cause of DSMAX in this family. The syndrome in this family may be allelic to the juvenile distal spinal muscular atrophy first reported at this locus.

Cerebellar leukoencephalopathy: most likely histiocytosis-related.

BACKGROUND: Histiocytosis, both Langerhans and non-Langerhans cell type, can be associated with cerebellar white matter abnormalities, thought to be paraneoplastic. The associated clinical picture consists of ataxia, spasticity, and cognitive decline. Hormonal dysfunction is frequent. MRI shows cerebellar white matter abnormalities, as well as brainstem and basal ganglia abnormalities. This so-called "neurodegenerative syndrome" may occur years before or during manifest histiocytosis and also years after cure. We discovered similar MRI abnormalities in 13 patients and wondered whether they could have the same syndrome. METHODS: We reviewed the clinical and laboratory information of these 13 patients and evaluated their brain MRIs. Seven patients underwent spinal cord MRI. RESULTS: All patients were isolated cases; 10 were male. They had signs of cerebellar and pyramidal dysfunction, behavioral problems, and cognitive decline. MRI showed abnormalities of the cerebellar white matter, brainstem, basal ganglia, and, to a lesser extent, cerebral white matter. Three patients had spinal cord lesions. Three patients had laboratory evidence of hormonal dysfunction. No evidence was found of an underlying metabolic defect. In two patients biopsy of nodular brain lesions revealed histiocytic infiltrates. CONCLUSIONS: Considering the striking clinical and MRI similarities between our patients and the patients with this neurodegenerative syndrome in the context of proven histiocytosis, it is likely that they share the same paraneoplastic syndrome, although we cannot exclude a genetic disorder with certainty. The fact that we found histiocytic lesions in two patients substantiates our conclusion. Patients with cerebellar white matter abnormalities should be monitored for histiocytosis.

Pelizaeus-Merzbacher disease: Genetic and cellular pathogenesis.

Pelizaeus-Merzbacher disease (PMD) and the allelic spastic paraplegia type 2 (SPG2) arise from mutations in the X-linked gene encoding myelin proteolipid protein (PLP). Analysis of mutations affecting PLP, the major protein in central nervous system myelin, has revealed previously unsuspected roles for myelinating glia in maintaining the integrity of the nervous system. The disease spectrum for PMD and SPG2 is extraordinarily broad and can be best understood by accounting not only for the wide range of mutations that can occur but also for the effects of PLP1 mutations on both cell autonomous and non-cell autonomous processes in myelinating cells. Appreciating the wide range of genetic and cellular effects of PLP1 mutations is important for patient and family counseling, understanding disease pathogenesis, and, ultimately, for developing future disease-specific therapies.

17p11.2p12 triplication and del(17)q11.2q12 in a severely affected child with dup(17)p11.2p12 syndrome.

Multiple congenital anomalies/mental retardation syndromes due to genomic rearrangements involving chromosome 17p11.2 include deletion resulting in Smith-Magenis syndrome and a reciprocal duplication of the same region resulting in the 17p11.2 duplication syndrome. We present the clinical and molecular analysis of an 8-year-old male with a dup(17p11.2p12) who was evaluated for unusual severity of the phenotype. Fluorescent in situ hybridization (FISH) analysis not only confirmed the 17p duplication but also identified an approximately 25% mosaicism for tetrasomy 17p11.2p12. Whole-genome array comparative genomic hybridization (aCGH) was performed to identify other genomic rearrangements possibly contributing to the severe phenotype and the unusual features in the patient. The 17p duplication was determined by FISH and aCGH to encompass approximately 7.5 Mb, from COX10 to KCNJ12. An approximately 830 Kb deletion of 17q11.2q12, including exon 1 of an amiloride-sensitive cation channel neuronal gene, ACCN1, was also identified by aCGH; breakpoints of the deletion were confirmed by FISH. Sequencing the non-deleted allele of ACCN1 did not show any mutations. Western analysis of human tissue-specific proteins revealed that ACCN1 is expressed not only in the brain as previously reported but also in all tissues examined, including heart, liver, kidneys, and spleen. The large-sized 17p11.2p12 duplication, partial triplication of the same region, and the 17q11.2q12 deletion create a complex chromosome 17 rearrangement that has not been previously identified. This is the first case of triplication reported for this chromosome. Our study emphasizes the utility of whole-genome analysis for known cases with deletion/duplication syndromes with unusual or severe phenotypes.

Steroid-responsive neurologic relapses in a child with a proteolipid protein-1 mutation.

A 10-year-old boy developed corticosteroid-responsive relapsing neurologic signs, including nystagmus and ataxia. MRI revealed multifocal T2 white matter hyperintensities; several were gadolinium-enhancing. CSF contained oligoclonal bands. Although the patient met criteria for multiple sclerosis (MS), the proteolipid protein-1 gene (PLP1) contained a mutation in exon 3B (c.409C>T), predicting a tryptophan-for-arginine substitution. This case raises questions about the role of inflammation in PLP1-related disorders and, conversely, PLP1 mutations in MS.

Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid-mediated excitotoxic axonal damage is attenuated in the absence of myelin proteolipid protein.

In vivo and in vitro studies have shown that alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor-mediated excitotoxicity causes cytoskeletal damage to axons. AMPA/kainate receptors are present on oligodendrocytes and myelin, but currently there is no evidence to suggest that axon cylinders contain AMPA receptors. Proteolipid protein (PLP) and DM20 are integral membrane proteins expressed by CNS oligodendrocytes and located in compact myelin. Humans and mice lacking normal PLP/DM20 develop axonal swellings and degeneration, suggesting that local interactions between axons and the oligodendrocyte/myelin unit are important for the normal functioning of axons and that PLP/DM20 is involved in this process. To determine whether perturbed glial-axonal interaction affects AMPA-receptor-mediated axonal damage, AMPA (1.5 nmol) was injected into the caudate nucleus of anesthetized Plp knockout and wild-type male mice (n = 13). Twenty-four hours later, axonal damage was detected by using neurofilament 200 (NF 200) immunohistochemistry and neuronal damage detected via histology. AMPA-induced axonal damage, assessed with NF 200 immunohistochemistry, was significantly reduced in Plp knockout mice compared with wild-type mice (P = 0.015). There was no significant difference in the levels of neuronal perikaryal damage between the Plp knockout and wild-type mice. In addition, there was no significant difference in the levels of glutamate receptor subunits GluR1-4 or KA2 in Plp knockout compared with wild-type littermates. The present study suggests that PLP-mediated interactions among oligodendrocytes, myelin, and axons may be involved in AMPA-mediated axonal damage.

Juvenile onset Huntington disease resulting from a very large maternal expansion.

We report a 5(1/2)-year-old girl with a maternal family history of Huntington disease (HD), who presented clinically with unbalanced gait, impaired speech, and increasing difficulty with fine motor control. Onset of symptoms began at the age of 3(1/2) years. The suspected diagnosis of juvenile HD, based upon her family history, was confirmed by DNA analysis. At age 7, the patient died secondary to complications of her underlying disorder. Juvenile-onset Huntington disease is uncommon, predominantly transmitted by fathers and is always associated with very large expansions of the CAG repeat. Interestingly, this patient inherited a large CAG size expansion from her mother, who herself had symptoms of HD at the age of 18. Molecular analysis revealed that the mother had 70 CAG repeats whereas our patient had approximately 130 CAG repeats. This is the largest reported CAG expansion from a maternal transmission that has been confirmed molecularly and it demonstrates that very large expansions can also occur through the maternal lineage.